With recent advances in the computer technology, it became customary to use computer systems for presentation of live video from video cameras, X-ray detectors, infrared sensors, and other video capture devices. It is well-known in the art that, in order to present high quality video on the graphics display system, the frame rate of the latter must be synchronized with the frame rate of the incoming video stream. If there is no synchronization, a video artifact known as “tearing” occurs. Tearing, which becomes obvious on a highly dynamic video content, is caused by the next frame being written to graphics memory while a display controller is using it to display the previous frame.
To avoid tearing anomaly, the rendering of incoming video must be digitally synchronized with the display refresh rate by buffering incoming frames and using the vertical blanking signal of the display controller to update the graphic memory only during a vertical blanking interval. This results in an acceptable video quality in situations when the frame rate of the incoming video is significantly lower than the display refresh rate, but it creates another motion artifact known as “judder.” Judder is caused by a necessity to skip or duplicate a video frame in order to maintain display synchronization, and it becomes especially obvious when the incoming frame rate is close to the display refresh rate. Even a slightest discrepancy between the incoming frame rate and the display refresh rate will eventually result in dropped or duplicated frames. For example, if the acquisition frame rate is 60.2 and the display refresh rate is 60, this will cause a frame drop every 5 seconds.
A number of prior art techniques has been proposed to minimize judder anomaly, such as temporal averaging, frame interpolation, or motion estimation, but these techniques do not completely avoid motion discontinuities and they introduce other image processing artifacts. It is clear that, in order to present an artifact-free video on a computer monitor, the graphics display system must be genlocked, or electrically coupled, with the video source. However, it is rarely possible nowadays to genlock a computer display to a video camera due to several reasons:
(a) conventional PC display controllers do not support external synchronization;
(b) digital video cameras rarely provide an output synchronization signal;
(c) if more than one camera is in use, genlocking them with a display controller would require a complex electrical solution not feasible for a conventional PC user.
Based upon the foregoing, it should be appreciated that there is a need for a computer system that can display live video free of aforementioned artifacts from one or several video capture devices without resorting to complex hardware solutions.